The aim of this project is to investigate the role of circulatory antigens in the pathogenesis of Heymann nephritis (HN) of rat. The results of these studies are relevant to our long term goals of understanding the pathogenesis of human membranous glomerulonephitis (MGN) to which HN has a remarkable immunological, histological and clinical similarity. Specifically, following experiments will be carried out: I. Isolation of the circulatory antigens 53K, 70K, 110K, 150K, 200K, and 250K from normal rat serum. II. Characterization of these antigens including determination of specificity, molecular weights, isoelectric pH (pI), and avidity of the circulatory autoantibody for these antigens. III. Study whether the circulatory antigens bind to structure in the subepithelial region of the glomerular basement membrane (GBM) in order to explain the subepithelial (SE) deposits in HN. IV. Size and charge based characterization of circulatory immune complexes (CIC) containing the circulatory antigens formed at various stages of HN to understand the relationship of these properties of CIC to the formation of SE deposits. Methods will include immunofluorescence, lectin affinity chromatography, immunoaffinity chromatography, chemical coupling of antibodies to inert gel support, preparative polyacrylamide gel electrophoresis, (PAGE), rediolabeling, radioimmunoassay, radioimmunoelectrophoresis, sodium dodecylsulphate (SDS)-PAGE, gel filtration, isoelectric focusing, immunoprecipitation, light and electron microscopic autoradiography, sucrose density ultracentrifugation (SDG) and chromatofocusing. Standard parameteric and non-parameteric statistical methods will be used to analyze the data. These studies will enhance our knowledge about SE immune deposit formation in the kidney which produce considerable renal mobidity in humans.